Various modalities exist for the efficient transportation of petroleum products, such as crude oil, gasoline, chemicals, and natural gas. Pipelines, rail cars, tankers ships, and trucks all work in harmony in the transportation network to deliver energy to the consumer. North America alone depends on over 185,000 miles of liquid petroleum pipelines, 320,000 miles of gas transmission lines, and more than 2 million miles of gas distribution pipelines. These pipelines constitute the dominant mode of petroleum product transportation.
Ideally, the pipeline is constantly transporting petroleum products with little or no downtime, but transportation may stop for maintenance or repair. Further, some pipelines are taken out of service when no longer needed. In these situations, it is sometimes necessary to remove the petroleum products from the pipeline.
One method for the removal of liquid petroleum from a pipeline is by pumping. This is problematic when the liquid diminishes to a level such that the pump mechanism begins to receive air or other gas causing cavitation. Various techniques are employed to prevent cavitation, for example, using a “pig” to flush the remaining petroleum through the pipeline and into the vacuum system. Pigs have significant drawbacks, however, because they are costly and time consuming to insert and remove from the pipeline. Another removal method is to insert a tube or pipe through a valve of the pipeline and attaching the vacuum system to the tube or pipe using a flexible tube. However, in order for the tube to fit through the valve and flange, the diameter of the tube must be less than the valve opening, which exposes the fluid within the pipeline to the environment, potentially allowing the escape of petroleum vapors into the atmosphere. Moreover, if the liquid within the pipeline is pressurized, then liquid may escape.